DESCRIPTION (adapted from investigator's abstract and/or aims): The applicant proposes to continue studies of the cellular mechanisms regulating gastric acid secretion. The are three specific aims in the current proposal. The first aim is to analyze the biochemical events in the pathway that couples the stimulus to parietal cell secretion. An attempt will be made to establish the role of protein phosphorylation in this pathway. The function of two phosphoproteins, one 80 kDa and the other 120 kDa will be examined in detail and the identity of other proteins associated with activation of acid secretion will be sought in a permeabilized gastric gland model. The second aim is to characterize the pathways for K+ and Cl- flux present in the apical secretory membrane of stimulated parietal cells. The characteristics of K+ and Cl- transport will be assessed in stimulated apical membrane vesicles. K+ and Cl- channel activity will be analyzed by reconstituting membrane proteins into lipid bilayers. The channel or carrier proteins will be purified and identified. The third aim is to characterize the recycling of membranes and proteins associated with the HCl secretory cycle. The components and functional activity of membrane domains during the secretory cycle will be identified and the nature of protein sorting during membrane recycling analyzed.